A meta-analysis of five randomised placebo-controlled trials involving 282 subjects found no significant benefits of cinnamon supplement on glycated haemoglobin (A1C), fasting blood glucose (FBG), or other lipid parameters.
And even when the researchers, from the University of Connecticut and Hartford Hospital, looked at various sub-groups, no apparent benefits were observed.
"Cinnamon does not appear to improve A1C, FBG, or lipid parameters in patients with type 1 or type 2 diabetes," wrote lead author William Baker in the journal Diabetes Care.
An estimated 19 million people are affected by diabetes in the EU 25, equal to four per cent of the total population.
This figure is projected to increase to 26 million by 2030.
In the US, there are over 20 million people with diabetes, equal to seven per cent of the population.
The total costs are thought to be as much as $132 billion, with $92 billion being direct costs from medication, according to 2002 American Diabetes Association figures.
The new meta-analysis challenges other studies that reported potential benefits of the spice.
A previous study by the U.S. Department of Agriculture reported in 2003 ( Diabetes Care , Vol. 26, pp. 3215-3218) that just 1g of the spice per day reduced blood glucose levels, as well as triglycerides, LDL cholesterol, and total cholesterol in a small group of people with type 2 diabetes.
A placebo-controlled, double-blind study published in 2006 ( Journal of the American College of Nutrition , Vol. 25, pp.
144-150) reported that cinnamon and a cinnamon extract (Cinnulin PF) could reduce blood pressure in spontaneously hypertensive rats (SHR).
Furthermore, a study published in the American Journal of Clinical Nutrition (June 2007, Vol. 85, pp. 1552-1556) reported that cinnamon could lead to slower emptying of the stomach and reduce the rise in blood sugar after eating.
However, there have been toxicity concerns over consistent consumption or high doses of whole cinnamon or fat-soluble extracts.
Indeed, two federal institutes in Germany recently called for cinnamon dietary supplements carrying health claims to reduce blood sugar and help control type-2 diabetes should be classed as 'medicinal products', and regulated as such.
The joint announcement from the Federal Institute for Medicinal Products and MedicalDevices (BfArM) and the Federal Institute for Risk Assessment (BfR) states their opinion that products marketed with a diabetes health claim should be classified as medicinal products and required to seek marketing authorisation.
The concerns came about from differing coumarin levels in some products, said to cause liver damage and inflammation when higher doses are taken over a longer period by sensitive individuals.
Source: Diabetes Care January 2008, Volume 31, Pages 41-43, doi: 10.2337/dc07-1711 "Effect of Cinnamon on Glucose Control and Lipid Parameters" Authors: W.L. Baker, G. Gutierrez-Williams, C.M. White, J. Kluger, C.I. Coleman